Chromatin and cytoskeletal tethering determine nuclear morphology in progerin expressing cells.

The nuclear morphology of eukaryotic cells is determined by the interplay between the lamina forming the nuclear skeleton, the chromatin inside the nucleus and the coupling with the cytoskeleton. Nuclear alterations are often associated with pathological conditions as in the Hutchinson-Gilford progeria syndrome (HGPS) where a mutation in the lamin A gene yields an altered form of the protein, named progerin, and an aberrant nuclear shape. Here, we introduce an inducible cellular model of HGPS in HeLa cells where increased progerin expression leads to alterations in the coupling of the lamin shell with cytoskeletal/chromatin tethers as well as with Polycomb-group (PcG) proteins. Furthermore, our experiments show that progerin expression leads to enhanced nuclear shape fluctuations in response to cytoskeletal activity. To interpret the experimental results, we introduce a computational model of the cell nucleus that includes explicitly chromatin fibers, the nuclear shell and the coupling with the cytoskeleton. The model allows us to investigate how the geometrical organization of chromatin-lamin tether affects nuclear morphology and shape fluctuations. In sum, our findings highlight the crucial role played by lamin-chromatin and lamin-cytoskeletal alterations in determining nuclear shape morphology and in affecting cellular functions and gene regulation.